The present invention concerns a hydrodynamic retarder specifically for installation in utility vehicles, and more particularly concerns a hydrodynamic retarder having a two flow working fluid cooling circuit between the outlet and the inlet of the retarder.
A retarder of this category is known from the German patent publication 22 38 726 (British patent 1,380,847). A compact-design retarder is joined there with a heat exchanger and a receiver for the working fluid in a common housing. The heat exchanger and the receiver are contained below the working space, another chamber for receiving leakage oil from the working space and the bearings is contained within the housing. Concerned is a retarder without a pump for filling the work space. The retarder is filled by pressurizing the receiver with compressed air, causing the entire line system to fill up with working fluid, with the rotor then assuming the circulation. The system empties again upon completion of the braking operation, with the rotor displacing the working fluid back into the heat exchanger and the receiver.
Previously known from the German patent document 35 45 660 and particularly FIG. 5 thereof (U.S. Pat. No. 4,773,513) is a retarder where the working fluid is recirculated as well without a pump, only by the impelling effect of the rotor. A line runs from the outlet on the retarder to a separately arranged heat exchanger and from there back again to the retarder. Working fluid from a separate receiver is fed into the circuit line for initiation of a braking operation.
What sets this prior retarder apart are specifically the manifold options for reduction of the air ventilation losses by injection of a fluid jet into the working space for generating an aperture type screen that prevents an energy-consuming torus vortex of air, specifically in the radially outer part of the working space. This peculiarity of the design according to FIG. 5 is constituted by the fact that the circulating mixture of air and working fluid entrains from the fluid surface in the heat exchanger just enough fluid to permit the formation of a fluid screen in the working space.
A disadvantage to this design is the fact that, while in a filling process the working space of the retarder is filled first, the lines to the heat exchanger, the heat exchanger itself and the return line must thereafter first fill themselves. Much valuable time passes before a superimposed pressure effective in terms of braking is generated within the retarder.
Also, the retarder according to aforementioned German patent publication 22 38 726, the entire line system must first be filled and subjected to superimposed pressure before the braking effect can fully set in. On the prior retarder with its compact design, this may perhaps be acceptable. However, with the retarder accommodated in the drive system of the vehicle in such a way that greater distances exist between the working space itself and the heat exchanger or the receiver for working fluid, a delayed and only gradual onset of the braking force of the retarder would be a grave operational disadvantage.
The problem underlying the invention is to provide a control system for a retarder which also in the case of spatial separation of the retarder from its heat exchanger assures also without a recirculation pump a swift availability and reliable operation in braking pauses, at minimal manufacturing cost.